UNIVERSITY  OF  CALIFORNIA      AGRICULTURAL    EXPERIMENT    STATION 
COLLEGE    OF    AGRICULTURE  benj.  ide  wheeler,  president 

THOMAS    FORSYTH    HUNT.    Dean  and  Director 

BERKELEY 


CIRCULAR  No.  85 
(February,  1913) 


A  PRELIMINARY  REPORT  OF  A  NEMATODE 

OBSERVED  ON  CITRUS  ROOTS  AND  ITS 

POSSIBLE  RELATION  WITH  THE 

MOTTLED  APPEARANCE  OF 

CITRUS  TREES 


BY 
E.  E.  THOMAS 


UNIVERSITY  OF   CALIFORNIA   PRESS 
BERKELEY 


INTRODUCTION 

The  citrus  growers  have  been  much  concerned  in  recent  years 
over  a  serious  trouble  of  a  very  obscure  nature  in  their  groves.  It 
has  attracted  attention  particularly  in  the  older  sections.  One  of  the 
principal  symptoms  is  a  light  mottling  of  the  leaves — it  is  probable 
that  this  symptom  is  only  one  of  the  characteristics  of  the  trouble. 
There  have  been  many  explanations  offered  for  this  disease,  or,  as  it 
has  generally  been  considered,  this  unhealthy  condition,  which  is  of 
so  indefinite  a  nature  as  hardly  to  be  called,  with  propriety,  a  single 
definite  disease.  People,  competent  to  offer  an  opinion,  have  stated  to 
me  their  belief  that  this  trouble,  generally  called  Mottled  Leaf,  is  by 
all  odds  the  most  serious  one  concerning  citrus  trees  in  California. 
Mr.  Thomas,  in  this  paper,  suggests  a  possible  cause  for  this  difficulty. 
As  to  whether  the  nematodes  he  mentions  really  constitute  the  sole  or 
principal  factor  in  mottled  leaf  remains  to  be  proven  in  a  final  way. 
The  fact  which  stands  out  from  Mr.  Thomas'  work  is  that  a  new 
nematode,  probably  new  to  science  and  certainly  new  in  its  relation 
to  the  orange  tree,  has  been  discovered. 

The  certainty  that  these  nematodes  penetrate  deeply  into  the  tissue 
of  the  feeding  roots  and  that  they  are  present  in  immense  numbers  is 
sufficient  evidence  that  they  must  injure  the  trees,  also  their  similarity 
to  the  destructive  nematode  of  the  beet  is  suggestive.  It  is  probable 
we  have  before  us  here  a  very  difficult  problem  and  one  which  will  take 
a  long  time  and  much  original  work  to  solve  properly.  The  first  step 
will  be  to  demonstrate  the  precise  relation  between  the  nematodes  and 
the  unhealthy  condition  of  the  orange  trees.  This  in  itself  will  require 
several  years,  in  my  judgment.  The  next  problem  will  be  to  study 
the  life  history  and  habits  of  these  nematodes  and  their  resistance  to 
various  agencies  which  can  be  brought  against  them. 

The  preliminary  investigation  recorded  in  this  paper  was  made  by 
Mr.  Thomas  in  connection  with  a  study  of  soil  texture  and  soil  moisture 
in  relation  to  mottled  leaf.  Data  had  accumulated  at  the  AVhittier 
laboratory  which  suggested  that  these  two  factors  had  something  to  do 
with  the  trouble,  and  the  work  of  making  systematic  and  accurate 
observations  had  been  assigned  to  Mr.  Thomas.  The  following  state- 
ment concerning  nematodes  and  their  possible  relation  to  mottled  leaf 
is  given  out  so  that  other  investigators  may  have  their  attention  called 
to  this  apparently  most  important  of  all  our  citrus  problems. 

Wm.  T.  Horne, 

Acting  Chief  Division  of  Plant  Pathology. 


A  PRELIMINARY    REPORT    OF    A    NEMATODE 

OBSERVED     ON     CITRUS     ROOTS     AND 

ITS  POSSIBLE  RELATION  WITH  THE 

MOTTLED  APPEARANCE  OF 

CITRUS  TREES* 

By  E.  E.  THOMAS 


SUMMARY 

1.  A  certain  very  obscure  disease  of  slow  or  retarded  development 
of  citrus  trees  exists  in  California.  The  most  characteristic  symptom 
of  this  disease  is  the  yellowing  of  the  leaves  between  tne  veins,  with  the 
green  color  only  along  the  mid-rib  and  the  lateral  veins. 

2.  A  particular  kind  of  nematode  which  has  not  before  been  de- 
scribed as  occurring  on  citrus  trees  has  been  been  found  associated 
with  this  disease.  Great  numbers  of  these  nematodes  pierce  the  smal] 
rootlets,  especially  of  badly  diseased  trees. 

3.  Although  this  is  but  a  preliminary  report  of  the  existence  of 
nematodes  on  citrus  trees,  yet  it  shows  that  they  may  be  an  important 
factor  in  the  growth  and  development  of  these  trees  and  justifies  a 
thorough  and  comprehensive  study  to  determine  the  existing  relation. 

Mr.  J.  R.  Hodges,  Horticultural  Inspector,  of  Covina,  California, 
has  found  nematodes  in  the  soil  scraped  from  the  roots  of  trees  with 
badly  mottled  leaves.  He  examined  some  of  the  diseased  trees  in  his 
district  and  came  to  the  conclusion  that  the  nematodes  injured  the 
roots  and  were  the  cause  of  the  disease.  Twice  previously  nematodes 
have  been  reported  in  connection  with  citrus  trees. 


*Acknowledgments. — In  presenting  this  article,  the  writei  wishes  to  express 
has  most  sincere  appreciation  of  the  hearty  cooperation  of  Mr.  D.  H.  White  of 
Whittier,  the  Covina  Valley  Farmers '  Club,  and  the  National  Orange  Company, 
of  Eiverside.  Mr.  A.  G.  Schulz,  of  Porterville,  has  also  given  his  assistance  at 
different  times.  Acknowledgment  is  here  given  of  the  work  of  J.  H.  Norton, 
formerly  of  the  Citrus  Experiment  Station  and  W.  M.  Mertz,  of  the  Citrus 
Experiment  Station,  who  conducted  the  fertilizer  experiments.  Special  mention 
is  also  due  Howard  S.  Fawcett,  Pathologist  of  the  State  Horticultural  Commis- 
sion. Mr.  Fawcett  not  only  collected  some  of  the  data,  but  otherwise  materially 
aided  in  the  work. 


The  common  injurious  nematode  {Heterodera  radicicola)  pene- 
trates the  roots  of  various  kinds  of  plants,  causing  galls  or  swellings 
to  form  where  it  enters,  and  reduces  the  vitality  of  the  plant  attacked. 
In  1889  these  knots  were  reported  on  citrus  roots  by  J.  C.  Neal,*  who 
states  that  the  orange  seedlings  are  affected  and  "when  the  tender 
shoots  first  appear  many  wither  and  die  at  once,  others  grow  vigorously 
till  the  end  of  the  first  season  when  they  are  usually  budded  with 
known  and  valuable  varieties  of  fruit.  The  next  spring  these  buds 
put  out  tardily  and  make  a  weak  growth,  the  leaves  become  spotted 
or  yellow,  then  drop,  the  bud  dies,  feeble,  straggling  shoots  sprout 
around  the  stem  which  maintain  a  sickly  vitality  till  the  first  drought, 
when  the  tree  dies,  and  on  examination  discloses  the  cause  in  the 
knotty,  decaying  roots,  without  rootlets  or  fibrillae." 

Nematodes  have  also  been  reported  on  citrus  trees  by  Gaston 
Lavergne.f  They  were  found  on  lemon  trees  which  were  very  badly 
injured  by  an  excessive  amount  of  water.  These  trees  were  planted 
very  close  together  and  the  ground  was  never  touched  by  the  sunshine. 
This  made  it  impossible  for  the  soil  to  dry  out  or  become  aerated.  The 
nematodes  were  Anguilulae  similar  to  Heterodera  radicicola  but  some- 
thing like  ten  times  larger.  Small  knots  were  found  on  the  roots  and 
in  these  the  young  nematodes  developed. 

Observing  that  the  mottled  trees  were  found  on  heavy  soil  as  well 
as  on  sandy  soil,  and  that  experiments  with  irrigation  and  fertilizers 
did  not  in  all  cases  have  beneficial  effects  upon  the  trees,  the  writer 
has  carried  on  an  investigation  in  different  districts  affected  with  the 
disease  to  see  if  the  nematodes  are  always  found  in  connection  with 
it.  An  examination  has  been  made  in  the  following  counties :  San 
Diego,  Orange,  San  Bernardino,  Riverside,  Los  Angeles,  Tulare, 
Fresno  and  Butte.  These  represent  the  most  southern  citrus  district 
of  California,  the  large  citrus  belt  around  Los  Angeles,  the  early 
orange  section  in  Tulare  County,  and  one  of  the  northern  districts. 

Groves  affected  with  the  disease  were  found  on  varying  types  of 
soil.  A  few  of  the  fibrous  roots  of  citrus  trees  were  taken  and  examined 
under  the  microscope  for  nematodes.  These  samples  were  taken  not 
only  from  badly  diseased  trees,  but  also  from  trees  slightly  affected 
and  from  good  trees  as  well. 


*  United  States  Department  of  Agriculture,  Bulletin  20,  Division  of  Ento- 
mology, page  12. 

fPublicationes  de  la  Estacion  de  Patolojia  Vejetal  de  Chile,  Num.  9  (Febrero 
de  1901). 


A  tabulation  of  the  results  follows : 

No.   of 

samples 

examined 

50 

Trees 
Valencia 

Root  Stock 
Not  known 

Type 
of  Soil 

Sandy 

Condition 
of  Tree 

Badly  mottled 

Nematode 
of  Roots 

Numerous 

5 

Valencia 

Sour 

Sandy 

Badly  mottled 

Numerous 

10 

Valencia 

Sweet 

Sandy 

Badly  mottled 

Numerous 

15 

Valencia 

Not  known 

Heavy  loam 

Badly  mottled 

Numerous 

5 

Pomelo 

Not  known 

Heavy  loam 

Badly  mottled 

Numerous 

5 

Navel 

Trifoliata 

Sandy  loam 

Badly  mottled 

Numerous 

160 

Navel 

Not  known 

Sandy  loam 

Badly  mottled 

Numerous 

15 

Navel 

Sour 

Sandy  loam 

Badly  mottled 

Numerous 

5 

Navel 

Sweet 

Sandy  loam 

Badly  mottled 

Numeroas 

22 

Navel 

Not  known 

Heavy  loam 

Badly  mottled 

Numerous 

2 

Navel 

Not  known 

Sandy  loam 

Badly  mottled 

Not  found 

4 

Lemon 

Not  known 

Sandy  loam 

Badly  mottled 

Found  numerous 

2 

Lemon 

Sweet 

Heavy  loam 

Badly  mottled 

Found  numerous 

55 

Valencia 

Not  known 

Heavy  loam 

Good 

Not  found 

30 

Valencia 

Not  known 

Sandy 

Good 

Not  found 

1 

Valencia 

Sweet 

Heavy  loam 

Good 

Found  in  large 
numbers 

4 

Navel 

Not  known 

Sandy  loam 

Good 

Few  found 

75 

Navel 

Not  known 

Sandy  loam 

Good 

Not  found 

55 

Navel 

Not  known 

Heavy  loam 

Good 

Not  found 

15 

Navel 

Sour 

Heavy  loam 

Good 

Not  found 

17 

Lemon 

Not  known 

Sandy  loam 

Good 

Not  found 

15 

Lemon 

Not  known 

Heavy  loam 

Good 

Not  found 

We  note  that  nematodes  are  not  confined  to  one  locality,  but  exist 
around  mottled  trees  in  all  of  the  districts,  and  that  out  of  the  300 
samples  examined  but  two  exceptions  occur.  In  all  the  samples  where 
the  nematodes  were  not  found,  a  much  closer  observation  was  made 
than  where  they  were  found,  and  with  the  result  above  tabulated. 

In  a  few  cases  nematodes  were  observed  around  good  trees,  but  with 
one  or  two  exceptions  they  were  in  small  numbers  in  comparison  with 
those  around  the  diseased  trees  in  the  same  grove.  If  they  are  dis- 
covered around  a  few  of  the  trees  in  a  grove  it  is  to  be  expected  that 
they  may  occur  on  the  surrounding  trees,  as  they  could  easily  be 
spread  with  the  irrigating  water,  rains,  the  cultivator,  etc.,  while  they 
may  not  yet  have  become  numerous  enough,  or  have  been  present  long 
enough  for  the  trees  to  show  the  effect  of  their  attack.  In  a  great 
many   cases   badly   diseased   groves   with   abundant   nematodes   were 


seem  adjacent  to  healthy  groves  in  which  ho  nematodes  could  be 
detected.  Our  observations  show  that  in  the  few  instances  where 
nematodes  are  found  in  apparently  healthy  groves,  the  worms  are  not 
at  all  prevalent  as  compared  with  the  diseased  groves. 

A  preliminary  study  was  made  to  learn  the  exact  relation  which  the 
worm  bears  to  the  root  tissue.  One  point  stands  out  very  clearly,  and 
that  is  the  fact  that  the  roots  do  not  develop  galls  or  knots,  so  far  as 
observed  by  us.  (Figs.  1,  2,  3,  4,  5,  6.)  This  is,  therefore,  different 
from  the  cases  noted  by  J.  C.  Neal  and  Gaston  Lavergne,  in  which  they 
state  that  galls  or  knots  were  found  on  the  roots. 


Fig.  1.     A  small  orange  rootlet  highly  magnified,  showing  a  group  of  nematodes, 
somewhat  out  of  focus  above  at  the  left,  and  a  single  one  at  the  right. 


Nematodes  sometimes  damage  the  root  of  the  host  directly,  not  only 
by  crawling  inside  the  tissues  and  causing  knots,  but  also  by  piercing 
the  root  with  the  mouth  parts  and  feeding  upon  it.  On  close  examina- 
tion of  our  specimens  it  was  found  that  many  of  the  nematodes  had 


pierced  the  root  and  pushed  their  way  into  the  tissues  for  quite  a 
distance.  In  some  cases  the  head  of  the  nematode  was  seen  to  have 
penetrated  six  cells  into  the  root  (Fig.  8,  also  3,  5  and  6).  Upon 
further  examination  it  is  found  that  the  number  of  nematodes  which 
pierce  a  rootlet  is  very  great.  In  some  cases  as  many  as  fifty  have 
been  counted  on  a  small  rootlet  one  inch  long. 

The  females  are  not  always  attached  to  the  root,  but  may  be  in  the 
soil  surrounding  it  and  seem  to  be  enveloped  in  a  gelatinous  or  slimy 
material.  A  number  are  generally  to  be  found  together  with  this 
gelatinous  material  surrounding  the  whole  group.    As  many  as  twenty 


Fig.  2.  Two  nematodes  on  a  small  orange  rootlet  highly  magnified.  These  are 
viewed  from  such  an  angle  that  they  appear  symmetrical.  Usually  the  tail 
appears  as  obliquely  placed. 


females  have  been  noticed  attached  to  the  root  in  one  group.  This 
bunching  or  grouping  not  only  occurs  with  the  females  but  is  also 
noticeable  with  the  males,  for  they  are  very  often  found  in  groups  of 
from  six  to  eight  or  more,  piercing  the  root  close  together.     Many 


groups  were  also  seen  in  which  there  were  >  both  males  and  females, 
with  the  anterior  portion  of  the  body  imbedded  in  the  tissues  of  the 
root.  Cross  sections  of  the  roots  were  made  and  the  nematodes  were 
seen  penetrating  the  tissue. 

In  observations  on  thirty-two  of  the  worst  deteriorated  orange 
groves  in  one  of  the  oldest  districts  in  the  state,  nematodes  were  found 
to  be  very  numerous  on  every  sample.  The  many  samples  examined 
from  each  tree  showed  the  nematodes  under  the  microscope  immedi- 
ately, although  these  were  only  little  pieces  of  the  rootlet  one  inch 
long  or  even  smaller.     Since  they  were  noted  in  such  great  numbers 


Fig.  3.  Transverse  section  of  a  citrus  rootlet  highly  magnified,  showing  a 
nematode  piercing  the  surface  and  penetrating  deeply.  The  head  of  the  nematode 
has  penetrated  nearly  to  the  point  of  the  arrow. 


on  the  tiny  rootlets,  one  would  conclude  that  there  must  be  millions 
of  nematodes  in  and  around  the  root  system  of  one  tree.  These 
diseased  groves  examined  are  as  bad  as  any  in  the  entire  state.  In  most 
cases  they  have  been  large  producers  in  the  past,  but  at  the  present 


time  they  are  giving  very  little  fruit  that  is  at  all  marketable  and  this 
is  of  an  inferior  quality.  In  most  cases  the  trees  thus  badly  diseased 
have  only  small  sickly  yellow  fruit  which  is  the  typical  condition  of 
badly  mottled,  deteriorated  trees. 

The  principal  symptoms  which  have  generally  been  recognized  in 
connection  with  mottled  leaf  or  "decadence,"  as  it  is  popularly 
called,  are  that  the  tree  fails  to  develop  normally,  but  grows  tall  and 
slender.  The  leaves  are  small  and  of  a  sickly  yellow  color,  or  they 
may  be  mottled,  the  veins  remaining  green  while  the  portion  between 
is  yellow  (Fig.  7).     Trees  only  slightly  affected  bloom  normally  and 


Fig.  4.     Orange  rootlet  highly  magnified,  showing  a  nematode  near 
the  center  of  the  field. 


10 

produce  good  fruit,  while  more  seriously  diseased  trees  often  bloom 
profusely  and  produce  small  fruit  of  a  pale  yellow  color.  Such  trees 
are  unprofitable.  Sometimes  only  a  portion  of  a  tree  is  affected.  In 
a  very  large  percent  of  cases  the  southeast  side  of  the  tree  has  been 
the  most  seriously  affected. 

Mottled  leaf  is  found  mostly  on  sandy  soil.  Many  instances  have 
been  noted  where  there  is  a  sandy  streak  running  through  a  grove,  and 
here  the  diseased  trees  occur,  while  the  rest  of  the  grove  which  is 
on  heavier  soil  may  be  in  a  healthy  condition.  The  moisture  content 
of  sandy  soil  varies  much  more  than  that  of  heavy  soil  in  the  same 


Fig.  5.     Transverse  section  or  orange  rootlet  highly  magnified,  showing  two 
females  and  one  slender  male  nematode  between  them. 


grove,  and  too  great  fluctuation  of  the  moisture  content  of  the  soil 
was  thought  possibly  to  cause  the  trouble.  Experiments  have  been 
carried  out  increasing  the  frequency  of  irrigations,  with  careful  de- 
terminations of  the  soil  moisture.  In  some  instances  some  improve- 
ment was  noted,  in  others  not.    Sandy  soil  is  also  supposed  to  furnish 


11 


the  best  conditions  for  the  growth  and  spread  of  nematodes,  provided 
the  soil  is  kept  in  good  condition  as  regards  moisture,  etc.  This  is  the 
case  in  an  orange  grove,  or  in  other  words,  what  would  make  the  best 
conditions  for  the  growth  of  the  orange  would  be  favorable  for  the 
nematode  as  well.  On  the  other  hand,  the  disease  is  not  very  often 
found  on  heavy  black  soil,  but  a  few  such  cases  have  been  noted  and 
in  each  case  nematodes  have  been   found  upon  the   roots,   in   large 


quantities  except  in  one  instance. 


Fig.  6.  Transverse  section  of  an  orange  rootlet  highly  magnified.  By  stain- 
ing with  eosin  the  course  of  the  anterior  part  of  the  body  was  clearly  shown. 
After  entering  the  root  the  worm  bent  strongly  toward  the  upper  side  of  the 
picture  and  again  strongly  inward  so  as  to  be  nearly  in  line  with  the  arrow,  and 
penetrated  nearly  to  its  point.  The  other  two  arrows  indicate  nematodes  of 
which  the  posterior  part  of  the  body  was  lost  in  preparing  the  section. 


One  of  the  trees  showing  mottled  leaf  in  heavy  black  adobe  was 
of  especial  interest.  It  stood  in  the  lowest  part  of  a  ten-acre  grove 
where  the  water  gathered  at  every  irrigation  from  the  whole  tract,  so 
that  the  tree  was  in  water-logged  soil  about  half  of  the  time.     In  and 


12 

around  the  roots  of  this  tree  the  nematodes  were  found  in  greater 
numbers  than  in  any  other  locality  examined. 

In  several  cases  the  owners  have  done  everything  they  could  to 
improve  the  trees,  trying  different  systems  of  pruning,  not  letting  the 
trees  dry  out,  using  commercial  fertilizers  liberally,  and  putting  on 
several  good  dressings  of  stable  manure,  but  all  apparently  to  no 
purpose,  for  the  trees  continue  to  get  worse  each  year.  The  trees  in 
these  groves  range  in  age  from  ten  to  twenty-five  years.  Practically 
none  of  the  younger  groves  are  bearing  in  the  same  way  as  these  older 
groves  did  when  they  were  at  the  same  period  of  growth.     The  soil  in 


Fig.  7.     Mottled  leaf.      Healthy  leaves  and   oranges  at  the  left  and  typical 
mottled  leaves  and  small  fruits  at  the  right. 


these  groves  varies  from  a  very  light  sand  to  a  sandy  loam  with  a  clay 
subsoil.  In  one  instance  the  fertilizer  was  applied  in  maximum 
quantities  and  a  large  number  of  different  substances  were  used  and 
all  the  possible  combinations  of  them.  They  were  applied  every  week 
and  the  results  carefully  noted.  The  trees  chosen  for  the  experiment 
were  typical  of  the  section  in  which  they  were  found,  and  two  and  one 


13 


half  years  after  the  experiment  was  begun  no  improvement  in  the 
mottled  condition  could  be  noted  in  any  case  by  comparison  with  the 
surrounding  trees.  In  some  instances  it  is  said  lime  has  had  a  beneficial 
effect,  but  the  trouble  has  been  found  in  its  worst  form  where  there 
is  an  excess  of  lime.  Temporary  improvement  is  noted  in  the  summer, 
but  the  writer  and  others  have  observed  that  the  mottled  leaf  shows 
much  worse  in  the  winter  months. 

The  nematodes  have  not  only  been  found  on  old  deteriorated  trees 
but  have  also  been  seen  on  the  roots  of  nursery  stock,  the  leaves  of 
which  are  mottled.  Doubtless,  therefore,  they  have  been  carried  from 
one  locality  to  another  in  the  soil  of  the  balls  surrounding  the  roots  of 
affected  nursery  trees. 

Aside  from  the  distribution  of  nematodes  by  infected  nursery 
stock,  there  are  many  other  ways  by  which  they  can  be  carried  from 
one  place  to  another.  The  irrigation  water  is  an  easy  means  of  scat- 
tering them,  also  the  cultivator,  and  they  may  be  in  the  soil  which 
adheres  to  the  wheels  of  a  wagon  or  the  feet  of  animals  and  in  these 
ways  be  spread  from  one  part  of  the  grove  to  another,  and  to  other 
groves  in  the  vicinity. 


Description  of  the  Nematodes 

As  yet  only  a  very  preliminary  and  incomplete  study  has  been  made 
of  these  nematodes,  but  the  following  characteristics  have  been 
observed : 


Fig.  8.  Drawing  of  a  section  of  an  orange  rootlet,  showing  a  nematode 
penetrating  to  near  the  point  of  the  arrow.  The  posterior  part  of  the  worm 
was  destroyed  in  cutting  the  section. 


14 

Both  the  male  and  female  nematode*  have  a  spear  which  aids  them 
in  piercing  the  root  {Fig.  8).  This  spear  varies  in  length  from  7  ^  to 
17  fx.  At  the  base  of  the  spear  is  found  the  slender  eosophagus.  No 
transverse  striae  or  hairy  appendages  have  been  noted. 

The  male  nematode  (Fig.  5)  has  a  length  varying  from  280  p  to 
420  ^  and  the  average  length  of  fifty  specimens  examined  is  340 /x. 
These  specimens  were  taken  from  four  localities.  At  the  point  of 
greatest  diameter  it  measures  from  10 /x  to  17/x,  with  an  average  of 
14  jx.    The  tail  is  long  and  tapers  to  a  point. 

Many  samples  of  rootlets  having  the  anterior  portion  of  male 
nematodes  imbedded  in  their  tissue  were  placed  in  water  and  examined 
under  the  microscope.  In  each  case  the  rootlet  had  been  carefully 
cleaned  with  a  brush  to  remove  the  soil  particles.  This  was  done  so 
that  the  nematodes  which  remained  could  be  examined  more  closely. 
The  posterior  portion  of  the  nematodes  thus  found  was  seen  to  move, 
showing  that  they  were  still  alive. 

The  male  nematode  while  frequently  found  with  the  anterior 
portion  of  the  body  imbedded  in  the  tissue  of  the  root,  more  often 
occurs  in  a  free  state  in  the  soil  surrounding  the  root. 

The  female  increases  in  thickness  until  when  mature  the  main 
portion  of  the  body  is  irregularly  elliptical  and  not  quite  symmetrical, 
the  posterior  portion  narrowing  abruptly  into  a  slender  obliquely 
placed  tail. 

The  adult  female  is  of  a  brownish  color.  The  posterior  portion  of 
the  female  is  on  the  outside  of  the  root  and  the  eggs  are  evidently 
deposited  outside  the  root  tissues.     Egg  laying  has  not  been  observed. 


